We will continue to analyze the structure and function of connections between mechanosensory afferents and identified interneurons in the abdominal nervous system of the crayfish. These studies will concentrate on 1) the basis for selective connections between afferents sensitive to a particular movement direction and certain interneurons; 2) the mechanism of presynaptic inhibition, mediated by two separate pathways onto the afferents; and 3) the nature of the interneurons that are direct antecedents to the afferents in the presynaptic inhibitory pathway. BIBLIOGRAPHIC REFERENCES: Wiese, K., Calabrese, R.L., and Kennedy, D. 1976. Integration of directional mechanosensory input by crayfish interneurons. J. Physiol. 39: 834-843. Wiese, K., Calabrese, R.L., and Kennedy, D. 1976. Integration of directional mechanosensory input by crayfish interneurons. J. Physiol. 39: 834-843.